How do you master the 'effortlessly cool' aesthetic without it looking forced?

I'm working on a new app interface and aiming for that coveted 'effortlessly cool' and minimalist feel, but every iteration ends up looking either too bland or overly complex. It's like I'm trying too hard to make it look like I'm not trying at all! What are your go-to principles or subtle tricks for achieving that genuinely understated yet impactful design?